English is missing a word. (Well, probably many words.) However, this is a really useful word: it's a gender-neutral singular pronoun for people.
In the good-old-boy days, they just said "he" but that's not cool anymore, nor should it be.
"It" is gender-neutral, but also implies a lack of humanity.
"He or she" is correct but oh-so-stiff. "S/he" is unpronouncable.
"They" tends to be my go-to, but is sometimes considered incorrect, since "they" implies more than one.
Personally, I'd love to see us expand use of the word "it" so that it didn't imply an object, so that the aliveness and dignity of its subjects came through clear, whether they were dogs, mountains, children, or silverware. However, our culture is pretty far from respecting the dignity of silverware. So in the meantime, what do we do?
There have been many attempts to add a gender-neutral pronoun to English, starting over a century ago. Wikipedia chronicles them here, along with much more details about the whole subject. This predicament came to my Carnation class's attention recently, while we were working on grammar, so I brought in the list of invented pronouns. Their favorites were "co" and "ze." We decided to try and use them all day.
We began by reciting the Emily Dickinson poem (#228) we'd been memorizing, gender-neutrally: Blazing in gold and quenching in purple/leaping like leopards to the sky/then at the feet of the old horizon/ ze lays zer spotted face to die. And so on.
It started off well, but like these experiments tend to do, faded out over time. And so we have to talk about unborn babies as its, and assign a gender to ambiguous strangers before we can talk about them gracefully. We slip into stereotypes too easily, calling doctors "he" and teachers "she" because it's easier. We use the singular "they" so often our ears can't hear its inconsistencies. And my young aspiring novelists still cannot write a novel without revealing the gender of their characters. Which is too bad, because that would be interesting.